Leishmaniasis is a major public health problem in Brazil, and we propose experiments that will advance our understanding of this disease with the specific goal of identifying new therapeutic approaches. This project involves collaboration between the University of Pennsylvania and the Federal University of Bahia, Brazil, and includes the study of patients that are treated at the Leishmaniasis Reference Center in Corte de Pedra, Brazil. L. braziliensis is associated with a strong inflammatory response that is the major cause of the disease, and we have begun to identify the major pathologic responses involved. We performed genome-wide transcriptional profiling of Leishmania braziliensis-infected cutaneous lesions and normal skin controls and identified over 2,000 differentially regulated genes. Pathway-level analysis of this transcriptional response revealed key biological pathways, as well as specific genes, associated with cutaneous pathology. This has allowed us to generate a testable 'metapathway' model of immune-driven lesion pathology, providing new insights for treatment of human leishmaniasis. The hypothetical meta- pathway derived from our genome wide transcriptional profiling analysis suggests that cytolytic cells within the leishmanial lesion promote cell death, leading to the release of inflammasome activating molecules. Consequent inflammasome activation promotes IL-1b production, thereby activating pro-inflammatory effector mechanisms that drive pathology. Our new preliminary studies indicate that NK cells play a large role in the cytolytic response, and in Aim 1 we will define the role of NK cells in mediating disease progression. Our preliminary data indicate that an NK cell activating receptor, NKG2D, is involved in NK cells induced cytolysis, and thus could be a target for therapy. In Aim 2 we will assess the role of IL-1b in promoting increased pathology and determine if IL-1b also represents a new target for immunotherapy. In addition to these studies, which focus on the development of new targets for immunotherapy, we will also attempt to define new biomarkers of treatment failure in patients. Thus, in Aim 3 we will define systemic transcriptional signatures, as well as cutaneous microbiome correlates, of disease severity. These will be the first studies to provide a broad understanding of systemic and local transcriptional changes, combined with a characterization of the skin microbiota at the lesion site. Taken together these studies will increase our understand of the mechanisms of immunopathology responsible for this disease, identify biomarkers that predict disease outcome in patients, and lay the foundation for proposing the use of new inhibitors as immunotherapy to promote clinical cure of the disease.